Objective When used to prolong life without achieving a benefit meaningful to the patient, critical care is often considered “futile.” While futile treatment is acknowledged as a misuse of resources by many, no study has evaluated its opportunity cost, that is, how it affects care for others. Our objective was to evaluate delays in care when futile treatment is provided. Design For 3 months, we surveyed critical care physicians in 5 intensive care units (ICUs) to identify patients that clinicians identified as receiving futile treatment. We identified days when an ICU was full and containedat least one patient who was receiving futile treatment. For those days, we evaluated the number of patients waiting for ICU admission more than 4 hours in the emergency department (ED) or more than 1 day at an outside hospital. Setting One health system that included a quaternary care medical center and an affiliated community hospital. Patients Critically ill patients Interventions none Measurements Boarding time in the ED and waiting time on the transfer list Main Results 36 critical care specialists made 6916 assessments on 1136 patients of whom 123 were assessed to receive futile treatment. A full ICU was less likely to contain a patient receiving futile treatment compared to an ICU with available beds (38% v 68%, p<0.001). On 72 (16%) days, an ICU was full and contained at least one patient receiving futile treatment. During these days, 33 patients boarded in the ED for >4 hours after admitted to the ICU team, 9patients waited >1 day to be transferred from an outside hospital, and 15 patients cancelled the transfer request after waiting >1 day. Two patients died while waiting to be transferred. Conclusions Futile critical care was associated with delays in care to other patients.